Prospect of graphite material in aerospace

1 Brush material

Brushes are mainly used in various engines, converters and motors, etc., which require good electrical conductivity, wear resistance and commutation function. There are two main types of electric brushes. One is graphite brushes made of resin or coal tar pitch as a binder and graphite powder and metal powder as materials, also called colored brushes; the other graphite brushes is made of carbon materials (such as graphite powder, coke powder, etc.) as the main raw material, also called black electric brush. The following mainly introduces 3 kinds of electric brushes. 

(1) TD27 black aviation brush

TD27 black aviation brush is a new type of aviation brush developed through two-stage production through technical cooperation with Russia and the introduction of advanced process equipment such as vibrating ball mill, lubricating material granulator and double-screw continuous extruder. This brush is characterized by good commutation performance, appropriate peripheral speed (up to 60 m/s), high rated current density (up to 30 A/cm²) and low wear. The flying height of the aircraft using this brush is more than 20,000 meters, the operating temperature can be greater than 200 ℃, and it has excellent "three defenses" capabilities. The main technical performance level of this product can be equivalent to the Russian product Γ27, indicating that the production and preparation technology of black aviation brushes in our country has reached a new level.

(1) TD32X black aviation brush

The brush used in the main generator QF-4.8 of the domestic French-imitation aircraft is a specially developed TD32X black aviation brush. The base material is a DZ type electric brush, which is processed through dipping, core filling and other treatments. This brush has excellent commutation performance and "three-proof" ability, and its service life is about 800 h. The service life of the brush is longer than the service life of the French 9020M black aviation brush.

(2) T2J5 colored aviation brush

The T2J5 colored aviation brushes suitable for large-capacity aviation starter generators are also specially developed. The brush has good commutation performance, low friction loss and extended motor service life, which is 1.5 times that of the original TJ5 brush. And the technical performance of the brush is much higher than the TJ5 brush, reaching the leading level.

2 Prospects for the application of graphite materials in the aerospace field

2.1 Sealing material

Due to its own defects, graphite has limited its application in the aerospace field. Through the improvement of graphite materials, the structure of graphite materials can be obtained with the characteristics of high strength, high density, fine particles, high purity, corrosion resistance, high temperature resistance and low pollution, which will be the development direction of graphite materials. In order to make the sealing material better meet the requirements of the aerospace field, the following aspects need to be paid attention to:

(1) Further strengthen the research on the impregnation mechanism of graphite materials. Understand the different mechanisms of impregnated graphite with different materials, such as the study of resin curing mechanism and metal percolation simulation, which can further match raw materials and carbon graphite products and adopt appropriate impregnation processes to achieve the best impregnation effect and obtain the best graphite suitable for sealing material.

(2) Pay attention to raw material selection. By studying the influence of different raw materials on the performance of graphite, we can improve the defects of the raw materials, improve the material technology, reduce the cost and shorten the production cycle, thereby reducing energy consumption.

(3) Strengthen applied environmental research. According to the requirements of different environments, the corresponding research and application are carried out to make it more detailed and specific; at the same time, the graphite composite material is continuously developed and researched to continuously improve its performance and expand the application range.

2.2 Throat lining material

At present, the graphite material of the throat lining is mainly the second-generation throat lining material, but the graphite matrix of the second-generation throat lining material has disadvantages such as low density and large ablation rate, which cannot meet the requirements of all small tactical bombs and high-pressure SRM throat linings. Therefore, it is necessary to accelerate the development of third-generation throat lining materials.

The main development direction of the third-generation throat lining material is to improve the ablation resistance and thermal shock resistance of the material to better suit the throat lining material. There are several suggestions for this:

(1) Choose the graphite material of needle-shaped petroleum coke. Needle-shaped petroleum coke materials have the characteristics of low thermal expansion coefficient and easy graphitization, so that the thermal conductivity and low thermal expansion coefficient of graphite materials are improved^[22-26], and the thermal shock resistance of the material can also be improved.

(2) Appropriate maximum particle size. At present, the maximum particle size of graphite materials with the best thermal shock resistance in foreign countries is 90 μm, while that in China is only 50 μm. Therefore, if the maximum particle size of domestic graphite materials can reach about 90 μm, the thermal shock resistance should be improved.

(3) Improve the degree of graphitization. Increasing the graphitization temperature can reduce the thermal expansion coefficient, increase the thermal conductivity, and improve the thermal shock resistance of the graphite throat lining material.

(4) Appropriately control the density of graphite materials. Studies have found that the higher the density of graphite materials, the lower the ablation performance^[15], but the higher the thermal expansion coefficient. Controlling the density to about 1.80 g/cm³ can improve the thermal shock resistance of the material without making the thermal expansion coefficient too large.

2.3 Other materials

Graphite is rarely used in electric brushes and other aerospace fields, which requires the continuous development of new types of graphite materials such as multifunctional materials, composite materials, and nanomaterials to expand its applications in the aerospace field.

3 Conclusion

The research and development level of China's graphite materials can meet the basic needs of aerospace products, but there is still a certain gap at home and abroad. Researchers are required to continuously improve the comprehensive performance of graphite products in order to expand the application of aerospace services, get MORE related technical information contact us.